/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.ui;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;

import org.springframework.core.Conventions;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Implementation of {@link java.util.Map} for use when building model data for use
 * with UI tools. Supports chained calls and generation of model attribute names.
 *
 * <p>This class serves as generic model holder for Servlet MVC but is not tied to it.
 * Check out the {@link Model} interface for an interface variant.
 *
 *
 * map对象存放内容: key: 属性值名称, value: 属性值
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @see Conventions#getVariableName
 * @see org.springframework.web.servlet.ModelAndView
 * @since 2.0
 */
@SuppressWarnings("serial")
public class ModelMap extends LinkedHashMap<String, Object> {

    /**
     * Construct a new, empty {@code ModelMap}.
     */
    public ModelMap() {
    }

    /**
     * Construct a new {@code ModelMap} containing the supplied attribute
     * under the supplied name.
     *
     * @see #addAttribute(String, Object)
     */
    public ModelMap(String attributeName, @Nullable Object attributeValue) {
        addAttribute(attributeName, attributeValue);
    }

    /**
     * Construct a new {@code ModelMap} containing the supplied attribute.
     * Uses attribute name generation to generate the key for the supplied model
     * object.
     *
     * @see #addAttribute(Object)
     */
    public ModelMap(Object attributeValue) {
        addAttribute(attributeValue);
    }


    /**
     * Add the supplied attribute under the supplied name.
     *
     * @param attributeName  the name of the model attribute (never {@code null})
     * @param attributeValue the model attribute value (can be {@code null})
     */
    public ModelMap addAttribute(String attributeName, @Nullable Object attributeValue) {
        Assert.notNull(attributeName, "Model attribute name must not be null");
        put(attributeName, attributeValue);
        return this;
    }

    /**
     * Add the supplied attribute to this {@code Map} using a
     * {@link org.springframework.core.Conventions#getVariableName generated name}.
     * <p><i>Note: Empty {@link Collection Collections} are not added to
     * the model when using this method because we cannot correctly determine
     * the true convention name. View code should check for {@code null} rather
     * than for empty collections as is already done by JSTL tags.</i>
     *
     * @param attributeValue the model attribute value (never {@code null})
     */
    public ModelMap addAttribute(Object attributeValue) {
        Assert.notNull(attributeValue, "Model object must not be null");
        if (attributeValue instanceof Collection && ((Collection<?>) attributeValue).isEmpty()) {
            return this;
        }
        return addAttribute(Conventions.getVariableName(attributeValue), attributeValue);
    }

    /**
     * Copy all attributes in the supplied {@code Collection} into this
     * {@code Map}, using attribute name generation for each element.
     *
     * @see #addAttribute(Object)
     */
    public ModelMap addAllAttributes(@Nullable Collection<?> attributeValues) {
        if (attributeValues != null) {
            for (Object attributeValue : attributeValues) {
                addAttribute(attributeValue);
            }
        }
        return this;
    }

    /**
     * Copy all attributes in the supplied {@code Map} into this {@code Map}.
     *
     * @see #addAttribute(String, Object)
     */
    public ModelMap addAllAttributes(@Nullable Map<String, ?> attributes) {
        if (attributes != null) {
            putAll(attributes);
        }
        return this;
    }

    /**
     * Copy all attributes in the supplied {@code Map} into this {@code Map},
     * with existing objects of the same name taking precedence (i.e. not getting
     * replaced).
     */
    public ModelMap mergeAttributes(@Nullable Map<String, ?> attributes) {
        if (attributes != null) {
            attributes.forEach((key, value) -> {
                if (!containsKey(key)) {
                    put(key, value);
                }
            });
        }
        return this;
    }

    /**
     * Does this model contain an attribute of the given name?
     *
     * @param attributeName the name of the model attribute (never {@code null})
     * @return whether this model contains a corresponding attribute
     */
    public boolean containsAttribute(String attributeName) {
        return containsKey(attributeName);
    }

}
